Integrated circuit devices have become essential components in a wide variety of products ranging from computers and robotic devices to household appliances and automobile control systems. New applications continue to be found as integrated circuit devices become increasingly capable and fast while continuing to shrink in physical size and power consumption. As more integrated circuit chips performing at least one electrical and/or optical function, and includes both single-chip and multi-chip devices. In multi-chip devices, each integrated circuit chip is usually separately fabricated or “built up” from a substrate, and the resultant chips are bonded together or otherwise coupled into a common physical arrangement.
Advances in integrated circuit technology continue toward reducing the size of electrical circuits to smaller and smaller sizes, such that an entire local electrical circuit (e.g., a group of memory cells, a shift register, an adder, etc.) can be reduced to the order of hundreds of nanometers in linear dimension, and eventually even to tens of nanometers or less. At these physical scales and in view of ever-increasing clock rates, limitations arise in the data rates achievable between different parts of the integrated circuit device, with local electrical circuits having difficulty communicating with “distant” electrical circuits over electrical interconnection lines that may be only a few hundred or a few thousand microns long.
To address these issues, proposals have been made for optically interconnecting different electrical circuits in an integrated circuit device. For example, in the commonly assigned U.S. 2005/0078902A1, a photonic interconnect system is described that avoids high capacitance electric interconnects by using optical signals to communicate data between devices.
As part of such optical interconnection schemes, optical coupling between planar waveguides located on different integrated circuit layers is often needed. In a simplest proposal applicable to inter-chip coupling, two chips are mounted side-by-side such that an edge facet of a first waveguide on the first chip directly abuts an edge facet of a second waveguide on the second chip. In another proposal, an optical fiber is used to transfer optical signals between the two edge facets of the different chips. In yet another proposal, an optical fiber is used to couple between a surface-emitting source on the first chip and a detector on the second chip, each chip having electrical-to-optical (E-O) and optical-to-electrical (O-E) converter(s) as necessary. However, issues arise for such proposals that limit their operational scalability (e.g., the number of optical interconnections achievable between chips) and/or the amount of achievable device compactness.
Vertical optical coupling schemes have also been proposed in which optical signals are transferred between facing layers of vertically arranged chips, the vertical arrangement providing for a smaller footprint while also accommodating a larger number of optical interconnections between the facing chips. Proposals include the use of angled reflecting structures and/or grating structures for urging vertical projection through an aperture on one layer and corresponding vertical collection into an aperture on the other layer.
Issues arise, however, in relation to one or more of optical coupling efficiency and optical crosstalk between different aperture pairs, especially as the vertical spacing between the facing layers is increased. Other issues arise in relation to one or more of electrical crosstalk among facing electrical elements, lateral area requirements of the vertical optical coupling subsystems, accommodation of vertical surface features on the facing surfaces, device complexity, alignment issues, and fabrication cost. Still other issues arise as would be apparent to one skilled in the art upon reading the present disclosure. It would be desired to provide for optical coupling between different layers of an integrated circuit device, whether such layers be all-optical or electro-optical, in a manner that addresses one or more of these issues.